In the conventionally used semi-molten molding method referred to as thixo-diecasting, scale (oxide film or the like) is formed on a surface of a starting cylindrical billet by exposing the billet to the air. Accordingly, when the billet is heated to a semi-molten state and formed into a product having a prescribed shape by extruding the semi-molten metal in a mold, there is concern that scale will be allowed to flow into the product section of the moid cavity, and internal defects will be formed.
The influx of scale into the product section of the mold must be prevented because of the concern that blowholes may form and/or a decrease in strength may be occur in the product by these internal defects.
In view of this, in the molding apparatus described in Japanese Patent No. 3686412, a gate component separate from the mold is attached to the section initially in contact with the billet inside of the mold in order to remove the scale near the surface of the billet. The gate component has a narrow-apertured through-hole, and the scale near the surface of the billet is removed when the semi-molten metal flows via the through-hole.